1. Field of the Invention
The present invention relates to a system for calculating exposure energy (Ee), and more specifically, to a system executing an exposure energy calculation program, using mask test data and a critical dimension (DC) specification to calculate the exposure energy.
2. Description of the Prior Art
The photolithographic process is the most important step in semiconductor fabrication. It transfers the layout of a designed integrated circuit onto a semiconductor wafer. In order to form the desired integrated circuits a mask is made, followed by a circuit design pattern being formed on the mask. A photolithographic process is used to transfer the circuit design pattern onto a photoresist layer on the surface of the semiconductor wafer. The critical dimension (CD) of the pattern transferred onto the photoresist layer depends on a number of factors, including mask quality, CD specification, exposure energy (Ee), machine type and operational parameters. As the complexity and integration of semiconductor circuits increases, the size of the circuit design pattern on the photoresist layer decreases. Therefore, precision of the critical dimension becomes more and more important.
CD error, leading to a lower yield and product quality, is one of the key areas that needs improvement in the production of semiconductor devices. From numerous experiments it can be concluded that the after development inspection critical dimension (ADI CD) relates to the transparency, the ratio of the patterning area to the developing area, of the mask. Thus, the critical dimension can be controlled by varying the exposure energy, based on the transparency of the mask chosen, without changing the layout on the mask.
Currently, the proper exposure energy is normally attained by analyzing data from numerous experiments. Thus, overexposure or underexposure at the corners of the design patterns on the photoresist layer, leading to a loss of resolution that causes end-of-line shortening of the design pattern and the difference between the pattern transferred onto the photoresist layer and the actual design pattern, is prevented.
However, this currently applied method is inefficient due to the tremendous amount of resources spent on experiments and the complicated processing of the experimental data. It is indeed an important objective to find an alternative method of obtaining the proper exposure energy more efficiently, and precisely so as to shorten the pilot run period, increase product reliability and improve scrap reduction.
It is therefore a primary object of the present invention to provide a system of calculating exposure energy (Ee) to replace the method currently used so as to improve production efficiency and reliability.
In the preferred embodiment of the present invention, the system of calculating exposure energy comprises an exposure apparatus and a control mean, comprising a processor and a data storing apparatus, electrically connected to the exposure apparatus. By supplying a mask value, comprising an actual transparency percentage parameter (Ta) and a mask error, and a critical dimension (CD) specification, comprising at least a basic transparency percentage parameter (Tb), a transparency constant (Tc), a CD energy constant (Cc) and a basic exposure energy, Tb, Tc, Cc and basic exposure energy is obtained after inputting a mask size parameter, a process name parameter, a layer parameter and a critical dimension parameter. An exposure energy calculation program is executed thereafter by subtracting the basic transparency percentage parameter (Tb) from the actual transparency percentage parameter (Ta) and multiplying together the resulting difference with the transparency constant (Tc) parameter to calculate a transparency percentage difference energy. A mask error energy is then calculated by multiplying together the CD energy constant (Cc) parameter with the mask error parameter. Finally the exposure energy is obtained by calculating the summation of the transparency percentage difference energy, the mask error energy and the basic exposure energy and transmitted to the exposure apparatus for the subsequent exposure process.
It is an advantage of the present invention against the prior art that the tremendous amount of resources spent on experiments and the efforts of onerous collecting, as well as the complicated calculation of the experimental data, can be saved. By settling the system for calculating exposure energy provided in the present invention, the proper exposure energy can be obtained more efficiently and precisely. The pilot run period can be thus be shortened with scrap reduction significantly improved, and the quality and the reliability of the product relatively increased as well.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings.